1. Field of the Invention
The present invention relates to an apparatus for decoding multiple moving picture signals and sound signals, and more particularly, to a decoding apparatus based on the MPEG (Moving Picture Experts Group) system.
2. Description of the Related Art
Prior to giving a description with regard to the conventional multiple picture/sound signals decoding apparatus based on the MPEG system, a general encoding method and apparatus will be explained.
To begin with, an interframe motion predicting method in the MPEG system will be described below with reference to FIG. 15. In this diagram, first a predictive-coded frame P0 is predicted from an intracoded frame I0. Subsequently a bidirectionally predictive-coded frame B0 is predicted from the two frames I0 and P0. And similarly another bidirectionally predictive-coded frames B1 is predicted from the intracoded frame I0 and the predictive-coded frame P0. For prediction of the bidirectionally predictive-coded frames B0 and B1, there are known three modes such as forward prediction from the predictive-coded frame P0, backward prediction from the intra-coded frame I0, and interpolative prediction executed bidirectionally as mentioned above. And in practice, the most adequate one for data compression is selected out of such three modes.
Hereinafter such intra-coded frame, forward predictive-coded frame and bidirectionally predictive-coded frame will be referred to as I frame, P frame and B frame, respectively. Now a description will be given on an exemplary apparatus for compression coding and decoding signals of multiple moving pictures and sounds by the MPEG system. FIG. 16 is a block diagram of a multiple picture/sound signals encoding apparatus which is capable of multiplexing and encoding three moving pictures and three sounds.
In FIG. 16, a digital moving picture signal V1 inputted to a terminal Ta is supplied via a compression encoder 1 and a buffer 2 to a multiplexer 13. Meanwhile, moving picture signals V2 and V3 inputted to terminals Tb and Tc respectively are supplied via compression encoders 3 and 5 and via buffers 4 and 6, respectively to the multiplexer 13. A sound signal A1 of the moving picture signal V1 is inputted to a terminal Td and then is supplied via a compression encoder 7 and a buffer 8 to the multiplexer 13. Similarly, sound signals A2 and A3 are supplied via compression encoders 9 and 11 and via buffers 10 and 12, respectively to the multiplexer 13.
Subsequently such signals are multiplexed by the multiplexer 13, whose output is then delivered via a buffer 14 to a terminal Tg and is further supplied to a storage medium or a transmission line. FIG. 17 shows an exemplary data arrangement of the output signal obtained from the terminal Tg. The three moving picture signals and the three sound signals thus compression-coded are multiplexed in the direction of the time base, as shown in FIG. 17. FIG. 18 is a block diagram of the moving picture compression encoder shown in FIG. 16. This encoder is of a general type equipped with a combination of a DCT (discrete cosine transformer) and an interframe predictor. In FIG. 18, a moving picture signal a fed to a video input terminal T1 is stored in a frame memory 21 and then is supplied to a subtracter 22 in the next stage. The output of the subtracter 22 is an interframe predictive difference signal which represents the difference between the input picture signal supplied to the positive terminal of the subtracter 22 and the predictive picture signal supplied to the negative terminal thereof.
The interframe predictive difference signal is supplied via a DCT 23 and a quantizer 24 to two transmission lines.
The signal from one transmission line is inputted to a variable length encoder 25 and then is multiplexed with motion vector data d and so forth in a multiplexer 26, and the multiplexed signal is delivered as an encoder output e from an output terminal T2 via a buffer 27. Meanwhile the signal from the other transmission line is processed in an inverse quantizer 28, an inverse DCT 29 and an adder 30, and then is outputted as a decoded picture signal b. Subsequently the picture signal b is inputted via a frame memory selector switch SW1 to frame memories 31 and 32.
A motion vector calculator 33 generates a motion vector d on the basis of the input data obtained from the frame memories 21, 31 and 32.
A predictive picture generator 34 generates a predictive picture signal c on the basis of both the motion vector data d obtained from the motion vector calculator 33 and the picture signal stored in the frame memories 31 and 32.
The predictive picture signal c is supplied to the negative terminal of the subtracter 22 via a switch SW2 while being supplied also to the adder 30 via a switch SW3. When the decoded picture signal b relative to the I and P frames, the switch SW1 is changed alternately so that local decoded picture signals of the I and P frames are supplied to the frame memories 31 and 32.
The switches SW2 and SW3 are closed in the P and B frames where the motion is predicted, and a subtraction and an addition for prediction of the picture are executed in the subtracter 22 and the adder 30, respectively. The switches SW2 and SW3 are open in the I frame where the motion is not predicted, so that none of a subtraction and an addition for prediction of the picture is executed in the subtracter 22 and the adder 30. FIG. 19 shows a conventional multiple picture/sound signals decoding apparatus which is complementary to the multiple picture/sound signals encoding apparatus of FIG. 16.
In FIG. 19, a multiplexed code obtained from a terminal Tg' is supplied via a buffer 35 to an inverse multiplexer 36, where the multiplexed code is separated into three moving picture signals V1, V2, V3 and three sound signals A1, A2, A3. And such signals are supplied to respective decoders. The moving picture signal V1 is supplied via a buffer 37 to a decoder 38, and the decoded signal therefrom is supplied to a D-A converter 39 where digital-to-analog conversion is executed. And the analog signal thus obtained is supplied to a display device 40. Similarly the moving picture signals V2 and V3 are supplied via buffers 41 and 45, respectively to decoders 42 and 46, respectively so as to be decoded.
The sound signal A1 is supplied via a buffer 49 to a decoder 50, and the decoded signal therefrom is further supplied via a D-A converter 51 to a reproducer 52. Similarly the sound signals A2 and A3 are processed in the same manner. FIG. 20 is a block diagram of each of the decoders 38, 42 and 46 shown in FIG. 19. A signal e fed to an input terminal T3 is supplied via a buffer 61 to an inverse multiplexer 62, where the signal e is separated into the quantized moving picture signal and the motion vector data d. The compression-coded moving picture signal is decoded to an interframe predictive difference signal by a variable length decoder 63, an inverse quantizer 64 and an inverse DCT 65, and then is supplied to an adder 66. The adder 66 receives, besides such difference signal, a predictive picture signal inputted thereto via a switch SW5 from a predictive picture generator 69 on the basis of the data obtained from the frame memories 67 and 68, so that the two signals are added to each other to produce a decoded picture signal.
The decoded picture signal thus obtained is stored in the frame memory 67 or 68 to become the data for producing a predictive picture signal while being inputted to a frame selection switch 70. The switch SW4 is changed every time the I and P frames are decoded, and the switch SW5 is closed in the P and B frames where the motion is predicted. The switch SW5 is open in the I frame, so that the output of the predictive picture generator 69 is not added by the adder 66.
In the frame selection switch 70, the decoded pictures are arranged in the display sequence and then are outputted to a terminal T4.
In decoding and reproducing the compression-coded signals of multiple moving pictures and sounds mentioned above, it is necessary to utilize multiple decoders, D-A converters, display devices and reproducers equal in number to the moving pictures and the sounds, as shown in FIG. 19. Therefore, the apparatus is rendered great in both structure and scale to be consequently inadequate for general use in particular.